1. Technical Field
The present invention relates to a sheet folding apparatus for folding a sheet with an image formed thereon, and more particularly, to improvements in the sheet folding mechanism for enabling a sheet to be folded in an accurate fold position with simplified structure.
2. Description of the Related Art
Generally, this type of sheet folding apparatus has been known as an apparatus for folding a sheet with an image formed thereon by an image formation apparatus such as a printing press, printer apparatus and copier in a predetermined fold position to perform finish processing. For example, Japanese Patent Application Publication No. 2008-247531 proposes an apparatus which is coupled to a sheet discharge outlet of an image formation apparatus, folds a sheet with an image formed for filing, and carries the sheet out to a subsequent binding processing apparatus.
The sheet folding apparatus for thus folding a sheet in half or one-third to carry out is configured as a post-processing apparatus of the image formation apparatus, or as a unit incorporated into the image formation apparatus or binding processing apparatus. Then, as a folding form, for example, for filing, various folding forms such as ½ folding, ⅓ Z-folding and ⅓ letter-folding are known corresponding to the intended use.
Then, the folding apparatus which is coupled to or incorporated into the image formation apparatus, binding apparatus (finisher apparatus, bookbinding apparatus) or the like is comprised of a folding processing mechanism and a transport mechanism for feeding and setting a sheet in the folding processing mechanism. For example, an apparatus is disclosed in Japanese Patent Application Publication No. 2008-247531 in which a collection guide for collating sheets that are fed sequentially in bunch form is provided with a roller pair that folds the bunch of sheets, and a folding plate disposed in a position opposed to the roller pair with a path therebetween inserts a fold of the bunch of sheets in a nip point of the roller pair.
Similarly, in Japanese Patent Application Publication No. 2007-320665 and Japanese Patent Application Publication No. 2008-007297, apparatuses are disclosed in which a pair of rollers and a folding plate (folding blade) are disposed in a path for feeding sheets, and the folding plate inserts a fold position of a sheet in a nip point of the pair of rollers to fold the sheet.
Then, with respect to transport members for feeding the sheet front end portion and rear end portion on the upstream side and downstream side of the folding rollers, the transport members are comprised of a front end stopper and a belt in Japanese Patent Application Publication No. 2007-320665. Meanwhile, the transport members are comprised of rollers in Japanese Patent Application Publication No. 2008-007297.
Then, control is performed to match the sheet velocity for inserting the sheet with the folding blade after the sheet fed to the fold position is once halted, the sheet velocity for folding the sheet with the pair of rollers, the sheet velocity for feeding the sheet with the transport member on the upstream side and the sheet velocity for feeding the sheet with the transport member on the downstream side with one another.
As described above, in the folding mechanism for inserting the fold position of the sheet in the nip between the rollers with the folding blade, unless the sheet velocity for inserting with the folding blade, the sheet velocity for folding with the pair of rollers, the sheet velocity for feeding with the transport member on the upstream side and the sheet velocity for feeding with the transport member on the downstream side are accurately matched with one another, there is a fear that the fold position is displaced, and the problem is known that each timing control becomes complicated.
Therefore, in Japanese Patent Application Publication No. 2005-008337, a folding mechanism is proposed in which a driven roller is disposed on the periphery of the roller positioned on the downstream side in the sheet transport direction between folding rollers in press-contact with each other to be movable between a waiting position and a press-contact position, and the driven roller is shifted from the waiting position to the press-contact position at timing at which the fold is formed.
According to this mechanism, the velocity for inserting with the driven roller, the velocity of folding rollers, and the sheet velocity for feeding with the transport member on the upstream side are the same (because of constituting with the same rollers), and the need for adjusting each velocity is eliminated.
Meanwhile, for example, in Japanese Patent Application Publication No. 2001-002317, Japanese Patent Application Publication No. 2008-184324, etc., it is disclosed that the blade shift velocity is set to be higher than the circumferential velocity of the folding rollers when a bunch of sheets is inserted in a pair of folding rollers in press-contact with each other with the folding blade and is folded.
Then, in Japanese Patent Application Publication No. 2006-290618 and Japanese Patent Application Publication No. 2007-015785, configurations are disclosed in which a deflecting member acts with opposite ends of the sheet nipped by a transport roller pair and a folding roller pair.